1. Field of the Invention
This invention relates to a preform for a fluorescent lamp for use as an indicating lamp so-called a single-end type fluorescent lamp, a fluorescent lamp prepared by the preform and a method for preparing the fluorescent lamp, particularly to a single-end type fluorescent lamp provided with a feeder unit at one end portion of a bulb to be suitable for use as an indicating lamp for an apparatus or a light emission element for an electric sign board.
2. Background Art
FIG. 4 shows the configuration of this type of a fluorescent lamp 90 for use as an indicating lamp of the prior art which is constructed by welding a bulb 91 whose inner surface is coated with a fluorescent material 92 to a stem 96 provided with a filament 93 coated with an electron emission substance 93a, a discharge electrode 94, and an exhaust pipe 95 in advance and exhausting inside air from the exhaust pipe 95, charging an inert gas 97 and mercury 98 into the bulb 92 and heat sealing this exhaust pipe 95 to seal the fluorescent lamp 90.
However, in the fluorescent lamp 90 for use as an indicating lamp of the prior art, since the sealing of the fluorescent lamp is achieved by heat-sealing the exhaust pipe 95, it is inevitable in the process that the exhaust pipe 95 projects from the stem 96. As the exhaust pipe 95 projecting from the stem 96 is easily cooled from the outside, the mercury 98 charged in the lamp tends to be liquefied in the exhaust pipe 95 having a lower temperature and to stay therein in a liquid state.
When the filament 93 is applied voltage to turn on the fluorescent lamp 90 for use as an indicating lamp, it takes a long time for the heat of the filament 93 to reach the mercury 98 in the exhaust pipe 95 located farther than the stem 96 from the filament and evaporate the mercury 98 thereby. As a result, a long time is required from the start of lighting until the characteristics of the lamp becomes stable.
In addition, since the exhaust pipe 95 projects, when an indicating unit, for example, is formed by mounting the fluorescent lamp 90 for use as an indicating lamp on a substrate, the exhaust pipe 95 may be broken by contacting it to the substrate and the fluorescent lamp 90 for use as an indicating lamp itself may be broken. Thus, a handling problem may occur.